If an individual is able to measure his pulse rate while jogging or running a marathon, for example, then he is able to monitor the amount of exercise performed as well as his physical condition (i.e., to avoid placing himself at risk). Accordingly, for this purpose, a portable pulse counter which can measure the user's pulse rate by being affixed to his arm is proposed. This type of portable pulse counter employs a photoelectric sensor to measure the pulse signal. The pulse rate is then determined by extracting the signal corresponding to the pulse from the pulse wave signal. However, a pulse wave signal obtained while the user is jogging includes a signal component generated by the user's body motion. Accordingly, it is not possible to extract the signal corresponding to the pulse without some correction for the body motion signal.
FIG. 12 is a block diagram showing an example of a conventional pulse counter disclosed in Japanese Patent Application First Publication No. Sho 60-259239. In addition to having a pulse wave detecting sensor 101, this pulse counter has a body motion detecting sensor 1003. The signals obtained from both of these sensors are subjected to frequency analysis at frequency analyzer 1002.
As shown in FIG. 13A, frequency analyzer 1002 converts the pulse wave signal detected by pulse wave detecting sensor 1001 to the spectrum expressed by waveform m. As shown in FIG. 13B, frequency analyzer 1002 converts the body motion signal detected by body motion detecting sensor 1003 to the spectrum expressed by waveform n. Here, waveform n is the result obtained after frequency analysis of the signal detected by body motion detecting sensor 1003. Accordingly, peak value B' expressing the fundamental wave component thereof represents the fundamental frequency of the body's oscillation. Thus, if the frequency of peak B' and the frequency of peak B in waveform m coincide, then the peak value B in waveform m is deemed to be the waveform due to the body's oscillation. The peak obtained by excluding peak value B from waveform m, i.e., peak A, the waveform corresponding to the pulse wave, can be read out.
FIG. 14 is a functional block diagram showing the structure of another conventional pulse counter. Pulse wave sensor 1201 detects the pulse wave in the body, and outputs the detected pulse wave signal to pulse wave signal amplifying circuit 1203. Body motion sensor 1202 detects body motion, and outputs the detected body motion signal to body motion signal amplifying circuit 1204.
Pulse wave signal amplifying circuit 1203 amplifies the pulse wave signal, and outputs it to A/D converter 1205 and pulse waveform shaping circuit 1206. Body motion signal amplifying circuit 1204 amplifies the body motion signal, and outputs it to A/D converter 1205 and body motion waveform shaping circuit 1207. A/D converter 1205 converts the pulse wave signal and body motion signal from analog to digital and outputs the result to CPU 1208. Pulse waveform shaping circuit 1206 shapes the pulse wave signal, and outputs it to CPU 1208. Body motion waveform shaping circuit 1207 shapes the body motion signal and outputs it to CPU 1208.
FIG. 15 is a flow chart showing the operation of the pulse counter shown in FIG. 14. As shown in the flow chart, the presence or absence of the body motion signal is confirmed, the pulse wave calculating method is switched, and the pulse rate is calculated and displayed. In FIGS. 14 and 15, CPU 1208 confirms whether or not a body motion signal is present based on the signal output from body motion waveform shaping circuit 1207, and switches the calculating method (step S1302). During the time that the body motion signal is being confirmed, the pulse wave signal and the body motion signal, which were converted from analog to digital signals (step S1303 and step S1304, respectively), are subjected to a fast Fourier transform (FFT hereinafter) (step S1305), and the pulse wave frequency component is extracted (step S1306).
When a body motion signal cannot be confirmed, the pulse wave is detected (step S1307), and the pulse waveform is subjected to rectangular wave conversion processing (step S1309). During this interval, CPU 1208 once again confirms whether or not body motion was present (step S1308). When body motion is not present, then the pulse rate is calculated from the rectangular wave without modification (step S1310). Because A/D conversion of the pulse wave and body motion are not necessary in this case, operation of A/D converting circuit 1205 is halted, as is the operation of multiplier 1210, which is required for FFT processing. Processing in CPU 1208 necessary for extracting the pulse wave is also halted. Thus, total consumption of electrical power can be reduced.
When body motion is present in step S1308, frequency analysis is performed using FFT processing (step S1305), and the pulse rate is calculated from the extracted pulse wave component (step S1310).
An exercise pitch measurer can also be formed having the same structure as the pulse counter shown in FIGS. 14 and 15. The frequency component of the exercise pitch is specified by body motion waveform shaping circuit 1207. This exercise pitch measurer can be used to inform the user of his running pitch, which is useful information for a runner. In addition, the distance of running can also be obtained from the running pitch and the stride length. An exercise pitch measurer and a pulse counter such as shown in FIGS. 14 and 15 have been disclosed in Japanese Patent Application First Publication No. Hei 7-227383, for example.
However, in the above-described conventional pulse counters, when a body motion signal is present such as shown in FIGS. 14 and 15 (steps S1302, S1308), then body motion detection is carried out all the time, and pulse wave component extraction processing (step S1306) to exclude the body motion spectrum from the pulse wave spectrum, and body motion pitch display (step S1407) are carried out. As a result, a body motion pitch is displayed even during exercise which does not have a periodicity, such as in the case of gymnastics. Moreover, conventional pulse counters perform pulse wave component extraction processing (step S1306) and display the body motion pitch (step S1407) regardless of whether or not noise is present in the detected body motion signal. As a result, an incorrect value may be detected for the body motion pitch, so that the body motion pitch and pulse rate displayed are less reliable.
In addition, conventional pulse counters perform the display of the pulse rate based on the pulse wave signal which is being detected at all times, irrespective of whether or not noise is present in the detected pulse wave signal (step S1303). Accordingly, when the user performs an irregular action, such as sudden action of the hand, the noise component in the spectrum of the pulse wave detection signal increases, increasing the probability of incorrect detection of the pulse rate. Thus, the reliability of the displayed value for the pulse rate falls.